1. Field of the Invention
The present invention relates to series or compound motors and, more particularly, to a plurality of motors having cross-coupled series-excitation for maintaining a balanced drive.
2. Description of the Background
Conventional AC or DC series excitation motors exhibit a specific characteristic, i.e., the rotational speed of the motor is inversely proportional to the square root of the torque. Hence, the rotational speed increases very fast under no load. When a load is driven by a series motors, and the load is unsteady, we usually need to prevent sudden load reducing which tends to accelerate the related series excitation motors during operation. This is especially true when the same load is jointly driven by two or more series motors, and an unsteady coupling relationship is formed between the load and the motors. In this case, the rotational speed of each respective motor will change suddenly, and this will further affect the stability of load. Compound motors may also exhibit this characteristic. For example, when conventional dual series-excitation or compound-excitation motors are used to drive the wheels of a loading machine, the ground coupling state will change and the motors will accelerate and decelerate intermittently, and poor operation will result.
U.S. Pat. No. 1,761,767 issued to Alexander shows cross-coupled generators which are used as brakes. The generators supply tapped resistances, and the resistance is progressively lowered to increase the braking action.
U.S. Pat. No. 2,763,823 issued to Symes uses cross-coupled motors to compensate for speed-differences. For instance, in a two-wheel differential gear-drive system, the cross-coupled compensates for the speed differential which occurs when the vehicle rounds a turn.
It would be greatly advantageous to adapt a cross-coupled configuration for AC or DC series excitation or compound-excitation motors which provides steady driving despite an unsteady load.